A laser system is now widely used in various fields, e.g. material processing, surface study, spatial optical information processing.
However, in a conventional laser system, an active resonator of the laser system oscillates simply in certain eigenmodes associated with a cavity formed by a pair of mirrors, so that the profile of the output beam produced by the conventional laser system is usually like a column; and it is hard to control the profile of the output beam. For example, if the output beam is, before focussing, interrupted by a board with a perforation, which has the same figure as the desirable profile of the beam cross section, then the output beam with desirable cross section is obtained. However, in that case some portion of the output beam is scattered by the board, and some energy of the laser, which was put into the cavity, is dissipated wastedly. It is also difficult to arbitrarily pick up a mode, which has a desirable beam cross section, from multi-modes excited in the resonant cavity, except for the lowest order mode, which has the profile like a column as mentioned above.
Accordingly, the object of the present invention is to provide a laser system, which makes it possible to control the spatial profile of the output beam without wasting any energy.
This and other objects and features of the invention will become apparent by reference to the following detailed description of preferred embodiments when considered in conjunction with the accompanying drawing.